JPH08211090A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To improve degree in design freedom of damping power by composing a magnetic damping mechanism of a pair of magnets causing resiliency. CONSTITUTION: When acceleration is applied upward, a mass part 1 is displaced upward. By this, the gap between a pair of magnets 6 and 7 disposed on the upper side is narrowed, so that the resiliency acting between the pair of magnets 6 and 7 is increased, so that the mass part 1 is pushed downward. When the acceleration is applied downward, the gap between a pair of magnets 6 and 8 disposed on the lower side is narrowed so that the resiliency acting between the pair of magnets 6 and 8 is increased, so that the mass part 1 is pushed upward. Thus, the mass part 1 is displaced in accordance with the acceleration applied from outside so that acceleration is detected, and, as an action suppressing the displacement of the mass part 1, the resiliency between two pairs of magnets 6 and 7, and 6 and 8 act, thus a damping action is caused against the displacement of the mass part 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
Particularly, it relates to the damping mechanism.

[0002]

2. Description of the Related Art In an acceleration sensor, a mass part that is displaced in response to an external force is supported by a beam part inside a frame, and a strain gauge detects the amount of strain generated by the displacement of the mass part to detect acceleration. There are a gauge system and a capacitance system that detects acceleration by detecting displacement of the mass section as a change in capacitance.

As a conventional damping mechanism in such an acceleration sensor, for example, there is an oil type one in which the viscosity of oil is utilized to give a damping action to the displacement of the mass portion. Further, there is an air system in which the damping force is generated with respect to the displacement of the mass part by compressing the air contained in the closed space by the movement of the mass part.

[0004]

In the conventional acceleration sensor of the oil type damping mechanism, when the acceleration sensor is used in an automobile or the like, the viscosity of the oil is such that the working environment temperature is −30 ° C. to + 100 ° C. It changes from 2 to 3 digits in the range. Therefore, on the low temperature side, the viscosity remarkably increases and the phase delay characteristic deteriorates significantly. Further, there is a problem that the viscosity is lowered on the high temperature side and the frequency characteristic of sensitivity is increased.

Further, in the air type damping mechanism, the viscosity of the air changes only about 3% even if the temperature changes by 100 ° C., and the temperature dependence of the damping force is small.
However, since the structure is such that air is compressed by a slight displacement of the mass part to generate a damping force, the gap between the mass part and the frame is narrowed, the area of the mass part is increased, or the air passage is narrowed. There is a problem in that there are structural restrictions such as such a frame body and mass part structure, and the degree of freedom in designing the damping force is low.

The present invention has been made by paying attention to such a conventional problem and has a high degree of freedom in designing a damping force without causing structural restrictions on a mass portion, a frame portion and the like. An object of the present invention is to provide an acceleration sensor provided with a magnetic damping mechanism in which the temperature dependence of damping force is extremely small.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 supports a mass part which is displaced according to an external force in a frame part by a beam part, and the beam part has the above-mentioned structure. In an acceleration sensor provided with a strain gauge that detects the amount of strain generated by displacement of the mass portion, a magnet pair that generates a repulsive force between both side portions of the mass portion in the displacement direction and the frame body portion is installed, The gist is that the pair of magnets constitutes a magnetic damping mechanism.

According to a second aspect of the present invention, a mass portion that is displaced according to an external force is supported by a beam portion inside the frame body portion, and the displacement of the mass portion is electrostatically disposed between the mass portion and the frame body portion. In an acceleration sensor provided with an electrode pair that detects as a change in capacitance,
A gist is that a pair of magnets that generate a repulsive force is installed between both sides of the mass portion in the displacement direction and the frame body portion, and the pair of magnets constitutes a magnetic damping mechanism.

According to a third aspect of the present invention, the mass portion that is displaced in response to an external force is held in the frame body in a floating state by the respective equilibrium repulsive forces generated in a three-dimensional direction by the plurality of magnet pairs, and the plurality of magnets are held. A pair of magnetic damping mechanisms are provided, and a plurality of electrode pairs are provided between the mass portion and the frame body to detect displacement of the mass portion in at least a two-dimensional direction as a change in capacitance. Is the gist.

According to a fourth aspect of the present invention, in the acceleration sensor according to the second or third aspect, two sets of the electrode pairs whose capacitance value increases or decreases relative to displacement of the mass portion in one direction are provided. The gist is that the differential output corresponding to the difference between the capacitance values of the two pairs of electrodes is provided as the detection output.

The invention according to claim 5 is the same as claims 1 and 2 above.
Alternatively, in the acceleration sensor described in 3, the gist is that the magnet pair is composed of a rare earth magnet.

[0012]

According to the first aspect of the invention, the mass portion is displaced according to the applied acceleration, and the beam portion is distorted. The amount of strain is detected by a strain gauge, and the magnitude of applied acceleration is detected from the rate of change in resistance. At the time of such acceleration detection action, the repulsive force of the magnet pair provided between the side of the mass part and the frame part on the side opposite to the direction in which the acceleration is applied increases, and the displacement of the mass part is suppressed to suppress the damping action. Occurs. Since the repulsive force of the magnet pair, that is, the damping force, freely changes according to the magnitude of the applied acceleration, the damping action effectively occurs from low acceleration to high acceleration.

According to the second aspect of the invention, the displacement of the mass portion according to the applied acceleration is detected by the electrode pair as a change in the electrostatic capacitance, and the magnitude of the applied acceleration is detected from the change in the electrostatic capacitance. . During such acceleration detection action,
The magnetic damping mechanism produces the same damping action as described above.

According to the third aspect of the invention, the applied acceleration in at least the two-dimensional direction is detected as a change in the capacitance, and the magnitude of the applied acceleration is detected. At the time of this acceleration detecting action, a magnetic damping mechanism corresponding to the applied acceleration in any of the dimensional directions works to effectively produce a damping action.

In the invention according to claim 4, two sets of electrode pairs whose capacitance values increase or decrease relative to the displacement of the mass part are provided on both sides of the mass part in the displacement direction, for example. By using the differential output corresponding to the difference between the capacitance values of the pair as the detection output, it is possible to obtain the detection output of double the magnitude and cancel the noise including the temperature drift.

According to the invention of claim 5, by forming each magnet pair with a rare earth magnet, the rare earth magnet has a very small change in the magnetic flux density with respect to the temperature change, so that the temperature dependence of the damping force can be remarkably reduced. It will be possible.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first embodiment of the present invention. In this embodiment, the acceleration detection unit has a cantilever structure and is a strain gauge detection system. First, the structure of the acceleration sensor will be described. The mass portion 1 that is displaced according to an external force is provided in the frame body 3 with the beam portion 2
A strain gauge 4 for detecting the amount of strain generated by the displacement of the mass portion 1 is mounted on the beam portion 2. Reference numeral 5 is a fixing member for fixing the beam portion 2 to the frame body 3. Further, a magnet 6 forming a part of the mass part 1 is integrated with the mass part 1 so that the beam part 2 becomes horizontal when the earth G is applied. The magnet 6 is magnetized in the thickness direction. For example, the upper side of the drawing is the N pole and the lower side is the S pole. Magnets 7 and 8 are arranged at the positions of the frame body 3 facing both poles of the magnet 6, respectively. The magnets 7 and 8 each have an S pole on the upper side and an N pole on the lower side.
At the poles, the opposing surfaces of the magnet 6 and the magnet 7 and the opposing surface of the magnet 6 and the magnet 8 have the same polarity to generate a repulsive force. It is configured. Rare earth magnets having small temperature characteristics are used as the magnets 6, 7 and 8, and the temperature is 10
Even if the temperature changes by 0 ° C., the change in the magnetic flux is only about 3%, and the temperature dependence of the damping force is significantly reduced.

Next, the operation of the acceleration sensor configured as described above will be described. When the acceleration to be detected is applied in the Z direction in FIG. 1 (the vertical direction in the drawing), the mass portion 1 is displaced according to the applied acceleration, and the beam portion 2 is distorted. This strain amount is detected by the strain gauge 4, and the acceleration is detected from the rate of change in resistance. During such acceleration detection operation, the magnetic damping mechanism operates as follows. When acceleration is applied in the upward direction, the mass unit 1 is displaced in the upward direction. Due to the upward displacement of the mass portion 1, the gap between the magnet pairs 6 and 7 arranged on the upper side is narrowed, the repulsive force acting between the magnet pairs 6 and 7 increases, and the mass portion 1 moves downward. Pushed to. When the acceleration is applied downward, the magnet pair 6 arranged on the lower side is
The gap between the magnets 8 is narrowed, the repulsive force acting between the magnet pairs 6, 8 is increased, and the mass portion 1 is pushed upward. In this way, the mass part 1 is displaced according to the acceleration applied from the outside, and the acceleration is detected. As a function of suppressing the displacement of the mass part 1, the repulsion between the magnet pairs 6 and 7 and 6 and 8 is performed. A force acts, and a damping action occurs with respect to the displacement of the mass portion 1.

As described above, according to the present embodiment, the damping force of the magnetic damping mechanism is freely changed according to the magnitude of the acceleration to be detected, that is, the magnitude of the displacement of the mass portion 1, so that ± 2 G is obtained. As a low G sensor or ± 50
A magnetic damping mechanism that functions as a high G sensor higher than G can be realized without extremely changing the structures of the mass portion 1, the beam portion 2, and the like. Further, the magnetic damping mechanism can function as a stopper that presses the mass unit 1 in a non-contact manner. That is, when excessive G is applied due to a drop impact or the like, a stopper is conventionally provided as a separate component in order to prevent the displacement of the mass portion and prevent the beam portion from breaking. However, in the present embodiment, the magnetic damping mechanism is provided. Since it can function as a stopper as it is and is a non-contact type, it does not cause damage to the mass portion, the beam portion, and the like.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, the acceleration detecting section has a cantilever structure and is of the electrostatic capacity type as in the above. 2 that are the same as or equivalent to the members and parts in FIG. 1 are designated by the same reference numerals as those used above, and duplicate explanations are omitted.
In this embodiment, both sides of the mass portion 1 in the displacement direction (see FIG.
Between the upper and lower parts of the mass part 1) and the frame body 3, circular electrode pairs 9a and 9b, 10a and 10b for detecting the displacement of the mass part 1 as a change in capacitance value are provided, respectively. There is. The electrode pair 9a and 9b form a capacitor C ₁ , and the electrode pair 10a and 10b form a capacitor C ₂ . The capacitance values of the _two capacitors C ₁ and C ₂ are converted into voltage signals by an AC bridge or the like and then input to a differential amplifier as shown in FIG. By taking the differential output corresponding to, the doubled detection output can be obtained. 11a and 11b and 12a and 12b are guard electrode pairs for fixing the stray capacitance, and are formed in a ring shape around the detection electrode pairs 9a and 9b, 10a and 10b, respectively.

Next, the operation of the acceleration sensor of this embodiment will be described. When the mass part 1 is displaced according to the magnitude of the applied acceleration, the electrode gap of one of the capacitors C ₁ and C ₂ is narrowed, and the electrode gap of the other capacitor is increased to increase the capacitance of both capacitors C ₁ and C _2. The capacitance value of is relatively increased or decreased. Since the electrode pairs 9a and 9b, 10a and 10b of the two capacitors C ₁ and C ₂ are symmetrically formed in the same shape, position and gap, the two capacitors C ₁ and C _{2 are}
The correlation of the change in the capacitance value with respect to the change in the electrode gap has the same characteristic. The capacitance values of the _two capacitors C ₁ and C ₂ are converted into voltage signals by an AC bridge or the like and then input to a differential amplifier to obtain a differential output, so that a double detection output can be obtained. Two more capacitors C ₁ and C
_{Since 2} is the same capacitor, the temperature drift at the zero point has almost the same characteristics, and the noise including this temperature drift is canceled by inputting it to the differential amplifier. During such acceleration detection operation, each magnet pair 6 and 7, 6
The damping action by 8 and 8 is substantially the same as in the case of the first embodiment.

3 to 5 show a third embodiment of the present invention. The present embodiment has a structure in which the mass portion floats in the internal space of the frame due to the magnetic repulsive force, and is a method of detecting acceleration in the two-dimensional direction by electrostatic capacitance. 3 and 4, 15 is a mass part, 16 is a frame body, and the mass part 15 is
Two pairs of magnets 17a and 17b, 18a and 18 in the X direction
Equilibrium repulsive force due to b, and two magnet pairs 19a in the Y direction.
And 19b, and 20a and 20b by the equilibrium repulsive force, and Z
Two pairs of magnets 21a and 21b, 22a and 22b in the direction
It is held in a state of floating in the internal space of the frame body 16 by the equilibrium repulsive force of. Two pairs of magnets 17a and 17b, 1
8a and 18b form a magnetic damping mechanism in the X direction, and two pairs of magnets 19a and 19b and 20a and 20b form a Y
Direction magnetic damping mechanism is configured, and two pairs of magnets 2
A magnetic damping mechanism in the Z direction is constituted by 1a and 21b and 22a and 22b. An electrode pair 23a for detecting the displacement of the mass portion 15 in the X direction as a change in electrostatic capacitance value is provided between both sides of the mass portion 15 in the X displacement direction and the frame body 16.
And a capacitor C ₃ and electrode pairs 24a and 24
The capacitor C ₄ composed of b is provided, and the mass portion 15 is provided between both sides of the mass portion 15 in the Y displacement direction and the frame body 16.
There is provided a capacitor C ₁ composed of electrode pairs 25a and 25b and a capacitor C ₂ composed of electrode pairs 26a and 26b for detecting the displacement in the Y direction as a change in capacitance value. Reference numeral 27 is a ground electrode short-circuit component, which is formed of a spring body. As shown in FIG. 5, the capacitance values of the two capacitors C ₃ and C ₄ for detecting the displacement of the mass portion 15 in the X direction are converted into voltage signals by the AC bridges 28c and 28d, respectively, and then converted into a differential amplifier 29b. By inputting the differential output corresponding to the difference between the two electrostatic capacitance values, a double detection output can be obtained. Similarly, the two capacitors C ₁ for detecting the displacement of the mass portion 15 in the Y direction,
The capacitance value of C ₂ is converted into a voltage signal by the AC bridges 28a and 28b and then input to the differential amplifier 29a so that a double detection output can be obtained.

The action of detecting the applied acceleration in the Y direction by the capacitors C ₁ and C ₂ and the action of detecting the applied acceleration in the X direction by the capacitors C ₃ and C ₄ are substantially the same as in the case of the second embodiment, and two sets are used. Of the pair of magnets 17a and 17b, 18a and 18b against the displacement of the mass portion 15 in the X direction and two pairs of magnets 19a and 19b, 20a and 20
The damping action for the displacement of the mass portion 15 in the Y direction by b is substantially the same as in the case of the first embodiment. In this embodiment, electrode pairs are provided between both side portions of the mass portion 15 in the Z displacement direction and the frame body 16.
A three-dimensional acceleration detection method can also be used.

[0024]

As described above, according to the first aspect of the present invention, the mass portion that is displaced according to an external force is supported by the beam portion inside the frame body portion, and the beam portion is displaced by the displacement of the mass portion. In an acceleration sensor provided with a strain gauge that detects the amount of strain generated in, a pair of magnets that generate a repulsive force between the both sides in the displacement direction of the mass portion and the frame portion are installed, and the magnet pair is used. Since the magnetic damping mechanism is configured, in the strain gauge type acceleration sensor, the magnetic damping mechanism has a relatively simple structure in which only a magnet pair is installed, and by changing the magnet material, shape, and magnetizing condition, leakage magnetic flux, In other words, since the repulsive force as the magnet pair is determined, the effect of having a high degree of freedom in designing the damping force can be obtained without causing structural restrictions on the mass portion, the frame body portion and the like.

According to the second aspect of the present invention, the mass part which is displaced according to the external force is supported by the beam part inside the frame body part, and the displacement of the mass part is provided between the mass part and the frame body part. In an acceleration sensor provided with an electrode pair that detects as a change in electrostatic capacitance, a magnet pair that generates a repulsive force between both side portions of the mass portion in the displacement direction and the frame body portion is installed,
Since the magnetic damping mechanism is composed of the pair of magnets, the magnetic damping mechanism in the capacitance type acceleration sensor has the same effect as described above.

According to the third aspect of the present invention, the mass portion that is displaced according to an external force is held in the frame body in a floating state by the respective equilibrium repulsive forces generated in the three-dimensional direction by the plurality of magnet pairs, and the plurality of the plurality of magnet portions are held. A magnetic damping mechanism is constituted by the magnet pair, and a plurality of electrode pairs for detecting at least two-dimensional displacement of the mass part as a change in capacitance are provided between the mass part and the frame body. The magnitude of the applied acceleration in at least the two-dimensional direction can be detected by the capacitance method with a simple structure. Further, the damping action can be effectively generated by the magnetic damping mechanism having the same effect as the effect of the invention according to the first aspect with respect to the applied acceleration in any of the directions.

According to the fourth aspect of the invention, the capacitance value increases or decreases relative to the displacement of the mass portion in one direction.
Since a pair of the electrode pairs is provided and the differential output corresponding to the difference in electrostatic capacitance value of the two pairs of electrodes is used as the detection output, in addition to the effect of the invention according to claim 2 or 3, It is possible to obtain a detection output having a size twice that of the detection output and cancel the noise including the temperature drift from the detection output.

According to the invention described in claim 5, since the magnet pair is composed of a rare earth magnet, the above-mentioned claim 1, 2 or 3
In addition to the effects of the inventions described, the rare earth magnet has a very small change in the magnetic flux density with respect to the temperature change, so that the temperature dependence of the damping force can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an internal configuration of a first embodiment of an acceleration sensor according to the present invention.

FIG. 2 is a configuration diagram showing an internal configuration of a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing an internal configuration of a third embodiment of the present invention.

4 is a cross-sectional view taken along the line AA of FIG.

FIG. 5 is a block diagram showing a differential output system using the capacitance of two sets of capacitors in the third embodiment.

[Explanation of symbols]

1,15 Mass part 2 Beam part 3,16 Frame body 4 Strain gauge 6,7,8,17a, 17b, 18a, 18b, 19
a, 19b, 20a, 20b, 21a, 21b, 22
a, 22b Magnets 9a, 9b, 10a, 10b, 23a, 23b, 24
a, 24b, 25a, 25b, 26a, 26b electrodes

Claims (5)

[Claims] 1. An acceleration sensor comprising: a mass part that is displaced according to an external force; and a beam part that supports the mass part in a frame part, and the beam part is provided with a strain gauge that detects a strain amount caused by the displacement of the mass part. , A pair of magnets that respectively generate a repulsive force between both side portions in the displacement direction of the mass portion and the frame body portion are installed,
An acceleration sensor characterized in that a magnetic damping mechanism is constituted by the magnet pair. 2. A mass part that is displaced according to an external force is supported by a beam part inside a frame part, and the displacement of the mass part is detected as a change in capacitance between the mass part and the frame part. In an acceleration sensor provided with an electrode pair, a magnet pair for generating a repulsive force is installed between both side portions of the mass portion in the displacement direction and the frame portion, and the magnet pair constitutes a magnetic damping mechanism. An acceleration sensor characterized by: 3. A mass part which is displaced according to an external force is held in a frame by a balance repulsive force generated in a three-dimensional direction by a plurality of magnet pairs in a floating state, and a magnetic damping mechanism is formed by the plurality of magnet pairs. A plurality of pairs of electrodes are provided between the mass section and the frame body to detect a displacement of the mass section in at least a two-dimensional direction as a change in electrostatic capacitance, respectively. . 4. Two sets of said electrode pairs whose electrostatic capacitance values increase and decrease relative to displacement of said mass part in one direction are provided,
The acceleration sensor according to claim 2 or 3, wherein a differential output corresponding to a difference in electrostatic capacitance value between the pair of electrodes is used as a detection output. 5. The acceleration sensor according to claim 1, wherein the magnet pair is composed of a rare earth magnet.